1. Field of the Invention
The present invention relates to an image forming apparatus such as a multifunction printer that includes a copying machine, a printer, a facsimile, and a plotter or includes at least one of them.
2. Description of the Related Art
While the demand on energy saving has been increased in recent years, there is a demand on the reduction in power consumption of an image forming apparatus. In particular, full color printing consumes a large amount of toner and uses large number of drive units. Accordingly, large power is required in the full color printing as compared with printing a black image (monochrome mode).
Japanese Patent Application Laid-open No. 2006-138930 discloses a method of printing in which a document image is detected and switching between color and monochrome outputs is automatically performed, in order to provide an image forming apparatus, which reliably saves expensive expendable supplies such as toner or ink and produces a copy as intended by a simple operation.
Further, in addition to an automatic mode switching means, provided is a preferential mode switching means, which forcibly switches it's mode to a monochrome mode in preference to the switching performed by the automatic mode switching means. The turning on and off of the preferential mode switching means are performed through an operation panel.
In Japanese Patent Application Laid-open No. 2004-341947, there is disclosed a structure where the surface of a main power switch is covered with a cover so as for an unnecessary operation of a switch not to be performed.
As in the method disclosed in Japanese Patent Application Laid-open No. 2006-138930, if the switching between a color mode and a monochrome mode is performed with the use of the operation panel or on the basis of the result from the detection of the document, it is natural that the switching between the color mode and the monochrome mode be performed according to the type of a document on all occasions.
Accordingly, the apparatus must always be ready to perform color output. For this purpose, correction of positional deviation among colors or density adjustment for each color should be always ensured.
Meanwhile, usually, most of output images are monochrome images and color outputs are only a little. That is to say, the color image forming apparatus in the related art frequently has performed correction of positional deviation of each color or density adjustment for each color, for the purpose of producing a little color outputs.
It takes time to perform the correction of positional deviation or density adjustment; and a machine cannot be used during that time. Further, such adjustment consumes toners of respective colors and requires driving of image forming units corresponding to respective colors. This incurs toner consumption and degradation of components of the units resulting from frequent driving of the units, and causes an increase in power consumption. Moreover, those are unexpectedly considerable.
Particularly, in recent years, a color product-printing machine, which enables mass production of outputs, has been proposed instead of an offset printing machine. However, in this field, there has been a strong demand on lengthening the life spans of components of each unit; reduction in toner and power consumption; and reduction in time during which a machine cannot be used to perform correction of positional deviation, as compared with the past.